Current biomechanical research techniques for developing "injury indices" involve conducting a series of impact tests on crash subjects (i.e. crash dummies or other human surrogates), obtaining characterizations of the subjects' impact resistance by instrumenting and/or observing their motion at a number of locations, and determining the extent and severity of the resulting pathophysiology by post-test physical examination. The "injury indices" are then developed by using statistical procedures to form relationships between engineering response parameters and the resulting "injuries".
Since both accurate injury characterizations and impact response data are desired from each test, the majority of current measurement schemes obtain data from instrumentation on the external surface of the subject. These measurement schemes, because of the limited technology available, have used either miniature accelerometers attached to the periphery of the subject to characterize the impact by a series of acceleration-time histories or high speed photogrammetric techniques to obtain relative velocities and displacements between various points on the body as functions of time. Invasive instrumentation, while having the prospect of providing a more precise and detailed characterization of local structural responses, invariably introduces artifactual trauma of its own either during installation or at the time of impact. Because this artifactual trauma is impossible to differentiate from the true impact-caused trauma, invasive instrumentation has not seen wide application.
The accelerometric technique has the advantage that it can be utilized in most automotive impact tests which include belts and enveloping compliant structures such as air bags and padding, an advantage that the photogrammetric technique does not have since visual contact cannot be maintained throughout many of these impact tests. A disadvantage of the accelerometric technique is that each sensor is attached to the subject at a given external point and will experience the subject's local rotations and translations at that point if any are present. The local rotations, while impact-induced, may not contribute to the "injury" and hence tend to obscure the data of interest.
The disadvantage of the photogrammetric technique is that when testing an enveloping compliant structure such as an air bag, the bag obscures portions of the subject shortly after it deploys. Post-test visual inspection will show the permanent "injuries" received by the subject, but film analysis cannot provide a documentation of the motions that produced the "injuries".
What is needed is a means of obtaining the shape of the periphery of a cross-section of a deformable body as it is being deformed by impact, such as in a car crash, by a means that does not introduce its own trauma to the body as with invasive instrumentation or that does not add extraneous data to its output as with accelerometric devices.
The patent to Caron et al, U.S. Pat. No. 4,729,174, shows a method of determining the deviation of a surface from its desired circularity. This differs from the present invention in several aspects, not the least of which being the fact that in Caron et al the surface being measured is presumed to be circular while in the present invention there is no presumption as to the shape of the surface being measured. Further, in Caron et al the measurements can only be made on a static surface while the present invention was specifically developed to determine the deformation of a surface during a short, severe impact.